Project Goals: The hypothesis to be tested is that vaccination against M. leprae with DNA vaccines and TB vaccines will (1) elicit a measurable immune response to appropriate antigens of M. leprae and (2) induce significant protection against a M. leprae challenge in the mouse footpad model. The DNA vaccines will also be tested for their ability to protect mice against challenge with virulent M. tuberculosis. Research Plan: The experimental design is to create and evaluate DNA vaccines expressing mycobacterial protein antigens known to elicit immune responses in humans infected with either M. leprae (ML) or M. tuberculosis (MT) and evaluate four newly created MT vaccines against leprosy. Specific-objectives are (1) prepare plasmid constructs (DNA vaccines) with genes expressing mycobacterial protein antigens and test immune response elicited by DNA vaccines delivered either by the intramuscular (IM) or intradermal (ID) route, (2) evaluate the efficacy of 4 newly developed TB vaccines for their protective efficacy against ML challenge in mice. The TB vaccines are: 1) leucine auxotroph of BCG, 2) leucine auxotroph of MT, 3) MT culture filtrate in adjuvant prepared from the nontoxic derivative of lipid A from Salmonella minnesota (MPL, [plus IL-2]) and 4) pooled MT genomic vaccine, (3) test protective efficacy, potency and immunotherapeutic potential of DNA vaccines in the mouse foot pad model for leprosy and (4) test the protective efficacy and potency of ML DNA vaccine against MT challenge. Mice will be immunized with test vaccines and immune responses will be monitored by lymphoproliferative, cytokine and systemic antibody responses. ML challenge will be in the foot pad-and MT challenges will be by aerosol and intravenous injection. Quantitative bacteriology will be performed on both protection models and histopathology of the immunization sites will be performed. Potency and immunotherapy of vaccines will be tested in the leprosy footpad model by monitoring induction of long-lived protection and effects of vaccines following ML infection, respectively. Significance: Leprosy is a significant public health problem globally with new case estimates of over one-half million yearly and a worldwide prevalence of approximately 1.26 million. Elimination of leprosy will most certainly require more than chemotherapy. A new vaccine for leprosy would provide the greatest potential impact for controlling and possibly eliminating the disease. New vaccines for TB and leprosy are being created using new technologies such as DNA vaccination and auxotrophic mutants of new and existing bacteria. This study proposes to create and evaluate new vaccines for leprosy and tuberculosis and determine their cross-protective efficacy for both diseases.